My initial thought is that night currency satisfies daytime currency, but what gives me pause is FAR 61.57(a)(2) notes that a non-current pilot is allowed to conduct day VFR or day IFR flights without passengers to obtain currency. There is no mention of night flight being allowed. This seems to imply that day flights are required for daytime currency.
Yes, night landings satisfy the requirements of §61.57(a)(1) for both nighttime and daytime currency.
The wording of the regulation is not crystal clear, and some (including me) have thought that the wording of (a)(2) required daytime landings for daytime currency. This is not the case, per the following interpretation from the FAA (Springfield, IL FSDO, dated 16 April 2014):
Other sources on the Internet agree with this interpretation:
Yes, night landings count for day currency.
Period. That's it.
Night currency limitations simply add an extra caveat to the above: you have to have done the landings to a full stop.
But what about 61.57(a)(2)? It clearly says day VFR or day IFR?
Your question is slightly misleading. (a)(2) talks about how to regain currency after you've already lost it...and the quote in your question is incorrect. You said this:
The reg actually says:
A non-current pilot is allowed to act as pilot in command in order to become current, so long as nobody is carried other than those individuals who are necessary for the conduct of the flight. Such as the first officer, a flight instructor, or an examiner.
So why is there the day limitation?
Because there's no restriction on multi-crew operations at night.
If you need to get current in a multi-crew airplane, you can. (a)(2) says so. You don't need to get current in a multi-crew airplane at night, because there's no restriction on multi-crew operations at night.
FAR 61.57(a)(2) is for the purpose of fulfilling (a)(1). Meaning, if you are out of day currency than you must make day landings. If are day current, then night landings will qualify to continue your day currency.